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Why does Double Clutching work

Discussion in 'The Hokey Ass Message Board' started by Dauphinee, Nov 18, 2012.

  1. Dauphinee
    Joined: May 15, 2011
    Posts: 79

    from New York

    Why is it that when I drive the 49 f1 I have to double clutch it to get it into gear?

    Is that how it was done years ago or do I need to have the transmission/clutch looked at?
  2. GREASER815
    Joined: Dec 2, 2008
    Posts: 973


    Old transmissions are unsynchronized. It works because it slows down the gears and makes it easier for them to mesh up again and they are not under a load.
  3. J'st Wandering
    Joined: Jan 28, 2004
    Posts: 1,682

    J'st Wandering

    Which gear?

    1st is not syncronized so that will have to be double clutched when down shifting. 2nd and 3rd have syncros so they should match up.

  4. jw johnston
    Joined: Oct 16, 2011
    Posts: 106

    jw johnston

    That trans should be synchronized. Sounds like the synchro rings or hub is worn out.

    Posted from the TJJ App for iPhone & iPad

  5. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,297

    Rusty O'Toole

    By double clutching you can bring the gears to the same speed. Then they slide into mesh without clashing. You may have synchronizers in the transmission but they are worn out or you have the wrong grease in the transmission.

    Old boxes before the sixties had non synchro first gear. You can shift from first to second because second has a synchro but if you go to shift down into first you must be careful.

    Real old boxes have no synchros at all. This was ok on low revving engines if you shifted slow, or if you knew to double clutch.

    First car with synchromesh, 1927 Cadillac. By the mid thirties everybody had it except trucks.
  6. bobj49f2
    Joined: Jun 1, 2008
    Posts: 1,798


    I think the heavy 3 speed is non-synchro, the lighter duty 3 speed are synchronized.

    My F-1 has the synchronized tranny, my F-2 doesn't. My youngest ground out the 1st and reverse gear a couple of years ago. I asked him if he didn't wait until the truck was stopped before he down shifted into 1st. He just gave me a stupid look and said, "Well, maybe."
  7. Hnstray
    Joined: Aug 23, 2009
    Posts: 11,583

    from Quincy, IL

    When double clutching on the upshift you can just double clutch and shift....when downshifting, i.e. 2nd to 1st, when you let out the clutch the first time you need to 'blip' the throttle to bring the gears closer in speed to avoid the clash before clutching the second time and engaging the gears. With a little practice (and luck to do no damage while practicing) you can perfect the technique and shift clash free at will.

    When I was a teen in the early '60's I drove a '55 Chevy 6 stick shop truck and managed to drive it all over, once under way, shifting up and down without using the clutch at all. just the shifter and the throttle...until I had to come to a complete stop and go again. If I found a kid doing that to my equipment today, I'd kick his behind :)

  8. I never use a clutch after initial start, unless I'm speed shifting. I learned to drive old non synchro simi's in the OLD Navy lol. I can run up or down including granny gear just shifting with RPM. it's hard to teach or learn unless you drive alot. but they just sllide in and out smooth as silk.
  9. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    from Wisconsin

    RPM matching is the way to shift. I learned to do it on farm tractors.
  10. 23reotim
    Joined: Feb 5, 2008
    Posts: 139

    from arizona

    my dad tought me how to drive stick like this. have been driving them this way every since. had a few people tell me that this is hard on the trans, but i have never tore one up. plus i figure a couple million truck drivers cant be wrong
  11. zibo
    Joined: Mar 17, 2002
    Posts: 2,346

    from dago ca

    I'll admit I was a VW guy way back when,
    and there is a book "how to keep your VW alive".
    It's one of the best mechanical books,
    as it taught how to get by in a pinch.
    Anyway the author John Muir wrote about that RPM matching trick,
    just in case your clutch cable broke or whatever.
    Such a good technique to use with any manual car.
    Great for model a's and any early 3-speeds,
    actually makes them more fun to drive.
    Like your on the cars level not fighting it.
  12. J'st Wandering
    Joined: Jan 28, 2004
    Posts: 1,682

    J'st Wandering

    Over the road truck transmissions do not have syncronizers.

    By not using the clutch, the syncronizers will try to get the speed of the two gears matched up but it will be going up against the speed of the motor. If the clutch is disengauged, the syncronizer speeds up or slows down the input shaft, not the motor.

    Over the long term, it can make a difference.

  13. dorf
    Joined: Dec 5, 2008
    Posts: 1,087

    from ohio

    its called speed for gears. when u run your vehicle pay attenion to your speedo ,each gear has a speed range and u work within those ranges for each gear.
  14. Ole don
    Joined: Dec 16, 2005
    Posts: 2,915

    Ole don

  15. C.R.Glow Neon
    Joined: Jul 16, 2009
    Posts: 221

    C.R.Glow Neon
    from stockton

    i started driving at 13yrs. of age in my '29 "A" pick-up, had to double clutch, best thing i ever learned(taught) on driving a car/truck, still do it in my healey/sprite with a 210 5-speed. RD
  16. propwash
    Joined: Jul 25, 2005
    Posts: 3,858

    from Las Vegas

    Drove my OT CJ5/LT-1/M21 all the way from near the top of the Cascade Mountains into the Jeep dealership one time when the clutch cross-shaft broke/fell off. Piece of cake if you know what you're doing. And that's through a few towns and many many traffic lights. Regardless of what folks say, if you do it right it is NOT 'bad for the trans' on any vehicle.
  17. 1951Streamliner
    Joined: May 15, 2011
    Posts: 1,874

    from Reno, NV

    Pardon my ignorance, but what is double-clutching and how do you do it?

    My '50 GMC never wants to downshift from 4th to 3rd, unless I'm going like 8 mph
  18. Bad Daddy
    Joined: Nov 13, 2010
    Posts: 829

    Bad Daddy

  19. Bigchuck
    Joined: Oct 23, 2007
    Posts: 1,141

    from Austin, TX

    I believe it goes like this: push in clutch pull out of gear, release clutch, push in clutch, put into gear, release clutch and go. Never had to do it my self. All my manual cars had syncronised transmissions.
  20. I agree, it's how I was taught (10 speed RoadRanger); it's how I drive today. Almost never use the clutch, even on my bike. Matching revs to speed.

    Think of it this way: with the clutch engaged, you have control over the input shaft speed with the throttle, the output shaft is controlled by the road speed, ie: not likely to change radically, or at all, really. When you let off to shift to neutral, the input shaft is still connected to the throttle. Let it rev down in a controlled manner (not all the way off the throttle, just mostly), then at the right time, put it into the next gear. A downshift is the same, just rev up instead of down.

    With the clutch DISengaged, you lose control over the input shaft speed, therefore you will need syncros to complete the shift.

    A note, though, diesels are a lot easier, as they rev more controllably, and there is usually about 500 rpm difference between gears at a given road speed.

    Further, most OTR drivers will shift progressively, that is, shifts will NOT occur at redline (2000-2500 rpm, typically), rather a 1-2 shift at 1100, 2-3 at 1200, 3-4 at 1300 and so on. This allows faster shifting, and keeps the engine in the meat of the torque curve, for faster accel.

    Yeah, I drove a truck for awhile...

  21. oldskooloutlaw
    Joined: Dec 3, 2008
    Posts: 223

    from Tulsa

    Sometimes something simple is overlooked, like pushing the clutch pedal all the to the floor instead of just enough to engage the gear.
  22. 270dodge
    Joined: Feb 11, 2012
    Posts: 742

    from Ohio

    I drove a 56 dodge for two months that had a blown clutch. You strart in gear and syncronize the speeds of the gears by a magical thing called feel. It aint somthing that can be easilly explained on a keyboard except to try to match the speed of the gears.Starting and stopping in town was the worst as you had to stop the engine and then restart when the light changed. Despirate times require despirate measures.
  23. kdf38
    Joined: Oct 8, 2008
    Posts: 10

    from Houston

    I had to drive a lot with broken clutch cables. The hard part was slowing down to try to get to lights when they had turned green and the other cars had started moving of cheating and almost stopping at stop signs. I' glad I never got stopped by the police for that.

    One Christmas Eve at about 7pm I loaded my VW Fox to drive 420 miles to the folks house. When I stepped on the clutch, the cable broke. I grabbed another one with a broken end and used some wire and epoxy to rebuild the end. I installed one end loosely and then tried to attach the cable to the pedal. It would not go on. I drove 420 miles with the broken cable. I had to stop when roadwork closed all but one lane. I waited for a long time trying to decide whether to cross the grass to the feeder road or not. Finally, I got a huge opening in traffic and started the car. I sped up to block anyone from getting in front of me and then slowed down to make sure that the traffic in front cleared so I would NOT have to stop in the only available lane. A big part of the trip was on multi-lane Hwys. I think on one trip I broke a cable on the way there and the replacement broke on the trip home. :( I must have replaced that cable a dozen times after the original broke. The original lasted a long time. The others mostly didn't. They ALL had plastic ends on them.
  24. 03GMCSonoma
    Joined: Jan 15, 2011
    Posts: 233


    I would put just a little pressure on the gearshift so when the RPMs matched up, it would slip right in gear. Watch your tach to see when it went into gear. Shifting down required you to increase your RPMs so the gears would match up. Again, note your RPMs and you will know when to shift. If you go this route, you certainly don't need to use your clutch. It works like feed through a goose.

  25. dan c
    Joined: Jan 30, 2012
    Posts: 2,150

    dan c

    i drove big trucks for 30 years--it's called "float shifting". after a while you get the hang of going up and down without a clutch. go through neutral and rev it a bit so the gears match road speed. when they came out with fully synchro transmissions, i hated them because they were so difficult to shift.
  26. uneasyrider
    Joined: Sep 23, 2012
    Posts: 163


    When I learned I learned that you weren't supposed to use the clutch (in a truck) unless you were starting or stopping. Later, when I took diesel mechanics, I was told that was hard on the transmission and you were supposed to use the clutch. I always thought the rig shifted better without it. I still play around in my cars to keep a little of the feel and up and downshift without the clutch. I guess it's hard on the synchros though if you don't use the clutch. I still do it now and then though. ;)
  27. Fordguy78
    Joined: Apr 2, 2009
    Posts: 558


    I know every now and then I have to double clutch for 1st in my '61 Merc 3-speed when I'm at a dead stop. If I don't it's a little bit of a fight. Then other times it drops right in.
  28. Rattle Trap
    Joined: May 11, 2012
    Posts: 358

    Rattle Trap

    I have been a truck driver for the last 32 years. I don't use the clutch unless I need to stop. I learned on a road ranger 10 spd tranny. Double clutching works too but it's not as smooth and a lot more work. Funny that this even came up because I was messing around double clutching today in my work truck. I don't even know why. Just something to break up the boredom.
  29. Interesting thread and nice to get real world input from some long term over the road truck drivers.
  30. Normbc9
    Joined: Apr 20, 2011
    Posts: 1,123


    I double clutch these when I drive them. Both have a five speed non-synchro transmission. The Sterling has a Hall-Scott 935 and I shft into 5th at 65 mph.

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